With increased number of small cell products and deployment thereof, the characteristics of radio products are likely to vary increasingly. Different radio products can have different receiver sensitivities.
It is envisaged that in the future 5G wireless communication systems will require multi-point transmissions using for instance distributed antenna systems (DAS). Increases in carrier frequency also cause increases in radio shadowing.
In DAS, antennas corresponding to a cell or a sector are no longer co-located, but are distributed in terms of locations.
FIG. 1 schematically presents a distributed base station 102 having a central power control 104 of a cell having distributed antenna sector i 106, antenna sector j 108 and antenna sector N 110.
The reason for using DAS may typically be a need to better cover a geographical region, which cannot be covered from a single location, and where it is desired to keep the connectivity to one specific sector/cell. More detailed reasons are however beyond the scope of the present application.
One example of a combined cell is to combine a radio dot system (RDS) with a DAS or an outdoor macro antenna sector. The RDS may have more than 20 dB higher noise floor level compared to macro products. Different indoor RDS cells may also have different noise floors levels depending on the length of the cable between the radio head in the sector and the corresponding radio unit, and the number of radio heads (or DOTs) in a cell.
A combined cell is a logical cell to which multiple antenna sectors belong. Antenna sectors belonging to a combined cell may either be located indoors or outdoors. The logical cell represented by the antenna sectors therein has the same Physical Cell Identity (PCI). The same cell level settings are hence used for all antenna sectors of the combined cell.
Combined cells may be used to combine macro sectors and small sectors, combine two or more indoor sectors, and/or to combine indoor and outdoor sectors, for instance.
Using a combined cell may reduce interference, improve radio condition and eliminate handovers between antenna sectors which else would have belonged to different cells.
When a combined cell has antenna sectors with different types of radio products, for example macro radio with micro radio or indoor radio, the receiver sensitivity of different antenna sectors may vary significantly.
A base station, for instance, an eNB, is capable to measure the power in a spectral band of UEs performing UL transmissions. The eNB can thus be considered to measure the sum of all powers received from UEs. These powers obey (1)P_total(t)=P_neighbor cells(t)+P_serving cell(t)+P_N(t),  (1)
where P_total (t) is the total power of the spectral band that is measured by the eNB, P_neighbor cells (t) is the sum of interfering power from UEs located in neighbor cells, P_serving cell (t) is the sum of the power from UEs located in the serving cell, and P_N (t) is the thermal noise floor power of the serving cell.
Equation (1) can be rewritten as equation (2)P_neighbor cells(t)+P_N(t)=P_total(t)−P_serving cell(t)  (2)
A base station measuring uplink signals, may thus subtract the power of UEs in the serving cell from the total power detected. However, the base station will not be able to distinguish the power contribution from UEs in neighboring cells from the power of the thermal noise floor, using equation (2).
The level of noise floors may however be estimated by applying an estimation of a soft minimum of a total received power, as calculated over a relative long time window.
Now, for a cell having multiple antenna sectors, the uplink power control target (P0) needs to be set to a value such that the UE can achieve a good uplink performance, i.e. a sufficient signal to noise ratio, typically above a certain threshold value, no matter which antenna sector the UE is connected to, and without introducing high interference.
By setting the P0 according to sector that has the highest noise floor causes the UE to output unnecessarily high power when it is connected to the sector that has a low (i.e. lower) noise floor, and thereby introduces interference to the neighbor cells. Also, outputting an unnecessarily high power will shorten the battery lifetime of the UE.
By setting the P0 according to the sector that has the lowest noise floor, may have the consequence that the UE is not able to get access to an antenna sector that has higher noise floor, due to that the power received in that antenna sector cannot overcome said higher noise floor. Also, sector selection based on received signal power will not be possible.
Moreover, by considering both antenna sectors that have relatively higher and lower noise floor levels, respectively, and setting the P0 to a value in between, has the drawback that it is difficult to tune and to find an optimal value. Also, the UE will experience a performance drop in the antenna sector with the higher noise floor, and create unnecessary high interference in the antenna sector with the lower noise floor.
There is therefore a need for determining an uplink power control target (P0) addressing the issues discussed above.